This invention relates to brazing into an assembly at least two members of different alloys, each having a metallurgical thermal capability different from the other. More particularly, it relates to brazing into an assembly such members in a high temperature operating turbine engine component such as a gas turbine engine combustor.
Designers of brazed assemblies of a plurality of members select for use in manufacture of the assembly one or more brazing alloys the highest required brazing temperature of which will not adversely affect any required member characteristic. Such selection preserves the integrity and usefulness of the brazed assembly. For example, a xe2x80x9cmember characteristicxe2x80x9d, as that term is used herein, that can be adversely affected by excessive thermal exposure include such xe2x80x9cmetallurgical featuresxe2x80x9d, as that term is used herein, as mechanical and/or physical properties, including but not limited to, grain growth, relief of work in the structure, incipient melting, solutioning of at least a portion of the alloy microstructure, recrystallization, reduction of strength and/or fatigue properties, etc.
In some desired assemblies, it has been recognized that at least one member requires use of a brazing alloy that has a brazing temperature greater than a temperature, herein called a xe2x80x9climiting temperaturexe2x80x9d, that will adversely affect a member characteristic. In one specific example, it was desired to use for a member in the brazed assembly of a gas turbine engine combustor, an alloy requiring a brazing temperature greater than a temperature at which excessive grain growth would occur in another of the members of the assembly.
One form of the present invention comprises a method for making an article assembly, and a preform, including a brazed joint. the assembly comprises a first member of a first substrate alloy having a limiting temperature above which at least one adverse member characteristic occurs adversely affecting at least one metallurgical feature of the first substrate alloy. The first alloy can be brazed with a first brazing alloy at a first brazing temperature less than the limiting temperature. Included in the assembly is a second member of a second substrate alloy requiring brazing at a second brazing temperature greater than the limiting temperature. One form of the method comprises the steps of bonding to a surface of the second substrate alloy a second brazing alloy that can be brazed at the second brazing temperature greater than the limiting temperature to provide a preform. Then the assembly is brazed to provide the brazed joint by brazing together the second brazing alloy and the first brazing alloy at the first brazing temperature less than the limiting temperature.
Another form of the present invention is an article assembly comprising a plurality of members and at least one brazed joint in the form of a multi-layered brazed joint. The assembly comprises the first member and the second member with a brazed joint at least at the second member. The multi-layered brazed joint comprises the second brazing alloy bonded to the second member, defining the preform, and the first brazing alloy bonded to the second brazing alloy.